Answer:

Explanation:
We know that:

where
is the initial energy,
is the final energy and
is the energy lost due to friction.
so:

Where M is the mass and V is the velocity of the runner, so:


As nouns the difference between magnet and lodestone
is that magnet is a piece of material that attracts some metals by magnetism while lodestone is a naturally occurring magnet.
Answer:
Part a)
here friction force will accelerate the box in forward direction
Part b)
a = 3.14 m/s/s
Explanation:
Part a)
When truck accelerates forward direction then the box placed on the truck will also move with the truck in same direction
Here if they both moves together with same acceleration then the force on the box is due to friction force between the box and the surface of the truck
So here friction force will accelerate the box in forward direction
Part b)
The maximum value of friction force on the box is known as limiting friction
it is given by the formula

so we have

now the acceleration is given as


Answer:
6.429 m/s^2.
Explanation:
Using equations of motion,
i. vf = vi + at
ii. vf^2 = vi^2 + 2a*S
iii. S = vi*t + 1/2 * (a*t^2)
Where,
vf = final velocity of the motion
vi = initial velocity of the motion
S = distance travelled
t = time taken to complete the motion
a = acceleration due to gravity
Given:
vi = 0m/s
vf = 45 m/s
t = 7 s
a = ?
Using the i. equation of motion,
vf = vi + at
45 = 0 + a*7
a = 45/7
= 6.429 m/s^2